NATO countries' heads of states and governments gather in Brussels for a one-day meeting

U.S. President Donald Trump and Britain's Prime Minister Theresa May react during a ceremony at the new NATO headquarters in Brussels

The trio posed for cameras before making small talk about Trump's trip.

Mr Juncker said he "had been following" Trump's travels around the Middle East with Mr Tusk saying the greeting in Saudi Arabia was "spectacular".

Meanwhile friends Angela Merkel, the German chancellor and former US president Obama appeared together at a talk called 'Being Involved in Democracy: Taking on Responsibility Locally and Globally' at Brandenburg Gate.

After Tusk and Juncker, it was French president Emmanuel Macron's turn to try and turn the President to his way of thinking.

Mr Macron hopes to prevent Trump from walking out on the Paris accord on climate change.

But the meeting appeared to get off to an awkward start.

Each man gripped each other's right hand so firmly that their knuckles turned white and their jaws seemed to clench.

Images from the photo session at the US ambassador's residence in Brussels showed Trump finally giving up, his fingers loosened while Macron is still holding on tightly.

The President of the United States has been cryptic over his true feelings on the EU, bouncing between calling it a "vehicle for Germany" and a "wonderful institution".

Mr Trump, who once labelled Brussels a "hellhole", have touched down in the city following his Middle Eastern tour for a first-hand look, and a NATO summit.

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Donald Trump (C) and US defence minister, James Mattis meets with Donald Tusk

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Donald Tusk met Donald Trump before leading him to meet heads of European Union institutions

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President Trump seemed more relaxed as he met Emmanuel Macron

He will be there for just 36 hours – but the events will make a big difference to relations going forward.

Pro-European chiefs have long been at odds with the nationalistic Trump regime, as they advocate single rules for multiple nations, and Mr Trump wants the US to come first.

The EU will want to hammer out difference with the US from trade to climate change.

At a summit of leaders of the Group of Seven (G7) world powers in Sicily on Friday and Saturday, Trump will be pressed to reaffirm the US commitment to free trade and to keep the United States in the Paris agreement on climate change.

The White House has said a decision on the climate deal will come after the visit.

Meanwhile, protesters were arrested outside the meeting.

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Donald Trump and Tusk gesture at each other before meeting

Thousands took to the streets of the city to protest the arrival of the Trumps.

A senior EU official said: “We all remember the mood which we had here not only in Brussels but all around Europe — that is anxieties and sometimes even fears on the direction which the new American administration will take, especially or in particular vis-a-vis the integration of the European Continent.”

Mr Trump himself appeared to be pro-Brexit and anti EU in the run-up to his election.

He openly spoke about countries quitting the bloc.

Streets were closed off for the arrival of Mr Trump and the First Lady who headed first to the Belgian royal palace to meet King Philippe and Queen Mathilde.

Mr Trump then met Prime Minister Charles Michel.

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Donald Tusk and Donald Trump looked tense entering the meeting

We have tried to avoid moving him around in an untimely way in Brussels

Spokesman

Michel’s spokesman, told POLITICO: “We have tried to avoid moving him around in an untimely way in Brussels."

Despite Mr Trump's comments on the capital in the past, Cauderlier said Trump's “first words were about his joy and pleasure to be in Brussels”.

Mr Trump and wife Melania are reportedly staying just a five-minute walk from the palace, across the Parc de Bruxelles.

There are three empty residences belonging to the US in Brussels since there is no United States ambassador to Belgium, to the European Union, or to NATO.

Donald Trump is due to meet European Council President Donald Tusk and European Commission President Jean-Claude Juncker this morning.

More campaigners are expected to take to the streets to vent their anger at the visit.

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Angela Merkel met with former President Obama on Thursday

A meeting with French President Emmanuel Macron is taking place before the president heads to the NATO headquarters this afternoon- an organisation he called "obsolete" – until his meeting with Jens Stoltenberg.

British Prime Minister Theresa May said on Thursday she would tell US President Donald Trump that intelligence shared between their two countries had to remain secure after leaks to US media about the Manchester attack.

May said she would talk to Trump at a NATO summit later on Thursday about the leaks, which included the publication of photographs of the bomb site by the New York Times.

The British prime minister touched down in Brussels Thursday afternoon.

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Donald Trump and Melania arrive in Brussels for round of meetings

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Donald Trump (2ndL) and first lady Melania Trump (R) pose with King Philippe and Queen Mathilde

An EU official told Politico: “I think now being in a situation where we can not address existential questions but talk about business, talk about cooperation, is in itself a measure of progress which took place in these last few months.”

Mr Trump said following the attack in Manchester where 22 Ariana Grande fans, as young as eight, were slaughtered by a suicide bomber.

The US president, who is travelling with the secretary of state, Rex Tillerson, added: “We have different problems to discuss, but number one is terrorism. We are in a terrible situation, but we will win.”

British Prime Minister Theresa May said on Thursday she would tell US President Donald Trump that intelligence shared between their two countries had to remain secure after leaks to US media about the Manchester attack.

May said she would talk to Trump at a NATO summit later on Thursday about the leaks, which included the publication of photographs of the bomb site by the New York Times.